The present invention relates to a responder, integrated circuit chip, non-contact IC card and device with no self-contained power supply in a non-contact IC card communication system, and a method of automatically adjusting the device with no self-contained power supply. More particularly, the present invention relates to adjustment of a resonance frequency in a device which performs an operation such as communication in an electrically non-contact state with another device by utilizing an electromagnetic wave.
Conventionally, a contact type IC card has been used for externally inputting/outputting data through an electrode of an IC (Integrated Circuit) embedded in a card. However, such contact type IC card must be inserted to a reading/writing device for input/output of data and is difficult to handle. Then, a non-contact IC card came into existence which performs electric power supply and data exchange using an electromagnetic wave. Such non-contact IC card is used, for example, for a gate at a station and a gate for a ski lift.
FIG. 19 is a circuit block diagram showing a structure of a communication system using such non-contact IC card. Referring to FIG. 19, the system includes an interrogator 50 (which is mounted for example in a gate for a ski lift), and a non-contact IC card 60. Interrogator 50 transmits a high-frequency carrier from an oscillating circuit (OSC) 52 via an antenna 55 under control of a controlling portion 51. When non-contact IC card 60 comes close to interrogator 50, the high-frequency carrier is received by an antenna (a coil) 61 of non-contact IC card 60. A power supply voltage generating circuit 64 converts the received high-frequency carrier to a direct current power for supply for the other circuit portion. Thus, non-contact IC card 60 can operate when it comes close to interrogator 50. It is noted that power supply voltage generating circuit 64, a modulating/demodulating circuit 65, controlling portion 66 and non-volatile memory 67 are included in an IC chip 68 so that a small size is achieved.
Information is transmitted from interrogator 50 to non-contact IC card 60 by modulation of the high-frequency carrier by modulating/demodulating circuit 53 under control of controlling portion 51. Non-contact IC card 60 demodulates the modulated high-frequency carrier by modulating/demodulating circuit 65. Controlling portion 66 receives the demodulated information for performing a necessary process such as rewriting of a content in non-volatile memory 67 and transmission of information.
Conversely, information is also transmitted from non-contact IC card 60 to interrogator 50. Here, an oscillating circuit is not provided on the side of non-contact IC card 60. Thus, the high-frequency carrier which has not been modulated is transmitted form the side of interrogator 50, and an impedance of a resonance circuit 63 including antenna 61 and a condenser 62 is changed by modulating/demodulating circuit 65 on the side of non-contact IC card 60. Interrogator 50 detects and demodulates the change in impedance as that of resonance circuit 56 on its own side including antenna 55 and condenser 54. Controlling portion 51 receives the demodulated information for performing a necessary process.
When non-contact IC card 60 is moved away from interrogator 50, the operation of card 60 stops because power is not supplied anymore. However, the stored information is retained even when power is removed as non-volatile memory 67 is used.
Thus, the communication system using non-contact IC card 60 is operated.
In the above described conventional technology, however, variation in authorized parts or the like makes the resonance frequency of resonance circuit 63 on the side of IC card 60 deviate from a design value, whereby IC card is not supplied with sufficient power. As a result, communication between IC card 60 and interrogator 50 is allowed only over a short distance, or in the extreme case, the operation thereof may not be allowed.
An object of the present invention is to provide a device which receives power supply from and communicates with the other device in a non-contact state and which is provided with a structure capable of suitably adjusting a resonance frequency of a resonance circuit.
Briefly speaking, a responder in a non-contact IC card communication system according to the present invention detects an output level of a resonance circuit by sequentially switching the resonance frequency of the resonance circuit by a switch circuit, and sets a switching manner of the switch circuit such that a desired output level is attained. Therefore, even when the resonance frequency is deviated from a suitable value due to initial variation in characteristic values of an antenna or condenser of the resonance circuit, the resonance frequency can automatically be adjusted to the suitable value for communication.
Preferably, a switching manner storing portion is provided which stores a preferred switching manner of the switch circuit. In this case, once the switching manner is stored, the resonance frequency needs not be sequentially switched for adjustment. Thus, an operation at the preferred resonance frequency can be rapidly performed.
More preferably, a reference voltage generating circuit is provided which receives an output voltage of the resonance circuit for generating a prescribed reference voltage. A magnitude of the output voltage of the resonance circuit in each switching manner is measured in accordance with the reference voltage. Thus, the output voltage of the resonance circuit is readily and correctly measured, thereby enabling correct adjustment of the resonance frequency.
More preferably, an output value storing portion is provided which stores an output value (measurement value) from the resonance circuit in each switching manner corresponding to the switching manner and, based on the stored content, a suitable switching manner is determined. Thus, the suitable switching manner is more readily and correctly determined.
More preferably, the switching manner which corresponds to the greatest output value is determined as the suitable switching manner. Thus, the resonance frequency can be adjusted such that the efficiency of the resonance circuit attains to the highest level.
More preferably, the output value is obtained every time the switching manner is switched and, when the output value exceeds a prescribed threshold value, the switching manner at the time is set as the suitable switching manner. Thus, automatic adjustment of the resonance frequency is rapidly performed.
More preferably, the switch circuit includes a plurality of transistors. Thus, the switching manner can readily and electrically be controlled for storage.
More preferably, the responder receives operation power from the resonance circuit. Thus, efficient power supply is ensured.
More preferably, communication of information is performed by the resonance circuit. Thus, efficient communication state is ensured.
More preferably, the suitable switching manner is determined during manufacture of the responder. Thus, even when the resonance frequency deviates from the design value due to variation in authorized parts or the like, a responder having a resonance circuit at a desired resonance frequency is readily manufactured.
More preferably, the suitable switching manner is determined once in a prescribed period of time. Thus, even when the resonance frequency changes due to secular change or change in ambient temperature, it is automatically adjusted to be back at a desired resonance frequency.
Further, briefly speaking, an integrated circuit chip used in a device with no self-contained power supply of the present invention detects an output level of a resonance circuit by sequentially switching a resonance frequency of the resonance circuit by a switch circuit, and determines and stores a switching manner of the switch circuit such that a desired output level is achieved. Thus, the resonance frequency is automatically adjusted to a suitable value, thereby enabling efficient power supply.
Further, briefly speaking, a non-contact IC card according to the present invention detects an output level of a resonance circuit by sequentially switching a resonance frequency of the resonance circuit by a switch circuit, and determines and stores a switching manner of the switch circuit such that a desired output level is achieved. Thus, the switching manner allowing a suitable resonance frequency can automatically be obtained for storage. In addition, once the switching manner is stored, it is not necessary to switch and adjust the resonance frequency any more, whereby an operation with at a preferred resonance frequency is rapidly performed. Further, a reference voltage generating circuit is provided which generates a prescribed reference voltage regardless of variation in output voltages of the resonance circuit, so that the output level of the resonance circuit in each switching manner is measured based on the reference voltage. Thus, the resonance frequency is readily and correctly adjusted in the non-contact IC card not having a power supply.
Briefly speaking, in a method of automatically adjusting a device with no self-contained power supply according to the present invention, an output level of a resonance circuit is detected while switching a resonance frequency of the resonance circuit by a switch signal, and the switch signal is applied to the resonance circuit such that the highest output level is achieved. Thus, the resonance frequency is automatically adjusted to a suitable value for efficient power supply.